The major purpose of this research is to characterize DNA polymerase activity responsible for the synthesis of nucleic acids in mammalian bone marrow and thymus. Quantitative measurement of one of these polymerases, terminal transferase, seems to be of value in the differential diagnosis of the type of leukemia present in human patients. It may also be a sensitive measurement of disease activity in certain leukemias and lymphomas. A prospective clinical study of the usefulness of terminal transferase in the diagnosis of leukemias and leukemic relapses is planned. Tissue culture systems for measurements of the effects of drugs and a variety of other agents on DNA polymerases, including terminal transferase, have been established. The tissue culture system is of use in identifying the role played by various DNA polymerases in programming lymphocytes for immunological functioning. BIBLIOGRAPHIC REFERENCES: M.S. Coleman and J.J. Hutton. Quantitation of Adenosine Deaminase Activity in cells from Human Peripheral Blood. Biochemical Medicine 13:46-55, 1975. M.S. Coleman, M.F. Greenwood, J.J. Hutton, F.J. Bollum, B. Lampkin, and P. Holland. Serial Observations on Terminal Deoxynucleotidyl Transferase Activity and Lymphoblast Surface Markers in Acute Lymphoblastic Leukemia. Cancer Research 36:120-127, 1976.